Color reproducing device

ABSTRACT

In a color reproduction device, an input profile that is referenced in converting an input image from an image input device into a device-independent color image is created based on image input device information, shooting- and observation-time lighting data, and subject data, allowing accurate conversion of the input image to the device-independent color image. In reproducing the image by an image output device, the spectral reflectance of the subject itself is calculated from image input device information and shooting-time lighting data, thereby reducing the effect of the shooting-time lighting. The colors of the subject under observation lighting are calculated from observation-time lighting data. A color reproduced image is estimated accurately on the basis of the subject data even if the input image has little information.

[0001] This is a division of U.S. patent application Ser. No. 09/149,906filed Sep. 8, 1998.

BACKGROUND OF THE INVENTION

[0002] The present invention relates to a color reproducing device whichtransfers accurately the colors of an image of a subject captured by animage input device to an output device.

[0003] Various attempts have been made hitherto to print or displaycolors as they are perceived by the human visual system.

[0004] As the performance of computers has been upgraded and their sizehas been reduced and with the spread of desktop publishing (DTP)systems, color matching techniques have been proposed for matchingcolors displayed on TV monitors and colors to be printed on printedmatter as an object of input and output (for example, U.S. Pat. No.5,739,928, Japanese Unexamined Patent Publication No. 6-51732, and soon).

[0005] A color management system (CMS), which is typical of the colormatching techniques, is equipped, as shown in FIGS. 32 and 33, with acolor corrector 3 between an image input device 1 and an image outputdevice 2. The color corrector 3 has an input profile 4 and an outputprofile 5 on the image input side (shooting side) and the image outputside (observer side), respectively. Input colors are first converted tocolors that do not depend on the image input device 1 and the imageoutput device 2 (hereinafter referred to as device independent colors)and then the matching of input and output colors is performed.

[0006] In U.S. Pat. No. 08/763,230, there is disclosed a color imagerecording and reproducing system in which, as shown in FIG. 34, an imagecaptured in a place remote from a place where it is reproduced istransmitted, and color matching is performed in spectrum to reproduce(display or print) colors accurately.

[0007] More specifically, in this system, a multi-spectral image of asubject is shot, and lighting spectral data when the image was shot andlighting spectral data at the time the image is reproduced are used toeffect conversion in such a way that, under lighting on the reproductionside, the spectral image of the subject is obtained as it was shot.

[0008] That is, the colors and gloss of the subject when it was shot arechanged to suit the reproducing lighting, allowing the state of thesubject when it was shot to be observed.

[0009] Next, a multidimensional spectral image is converted into athree-dimensional vector image composed of X, Y, and Z values and thentransmitted to the reproducing site. In the reproducing site, the imageis converted to color signals corresponding to the spectralcharacteristics of the reproducing device and then outputted to adevice.

[0010] The color corrected image is displayed on an output medium(monitor) of FIG. 34.

[0011] The output profile is created in accordance with the followingprocedure.

[0012] A monitor 131 and a chromaticity meter 132 are set in a place,such as a dark room, which is not affected by outside light. As shown inFIG. 35, predetermined RGB signals are generated by an RGB signalgenerator 133 and displayed on the screen of the monitor under thecontrol of a display controller 134. The colors displayed are measuredby the chromaticity meter 132.

[0013] The output signals of the chromaticity meter 132 are detected bya chromaticity detector 135 as chromaticity values such as XYZ values.The detected signals are then sent to an output profile computation unit136.

[0014] The output profile computation unit computes an output profilefrom the relationship between the RGB values generated by the RGB signalgenerator 133 and the chromaticity valued detected by the chromaticitymeter 135.

[0015] The relationship between the RGB values outputted to the monitor131 and the XYZ values outputted from the monitor 131 will be describednext.

[0016] The monitor has RGB phosphors that produce the three primarycolors, red, green, and blue, and produces a color image by excitingthose phosphors by electron beams modulated by R, G and B signals. Thevalues of the R, G and B signals (the RGB values) are produced by theRGB signal generator 133 of FIG. 35.

[0017] The RGB values are converted in a non-linear manner by the gamma(γ) characteristic of the monitor 131. Let the gamma characteristic ofthe RGB phosphors be denoted by γr[ ], γg[ ], and γb[ ], respectively.The colors produced by the RGB phosphors are combined by eye into acolor; thus, the chromaticity values (XYZ values) outputted from themonitor are represented by the sums of signal values each subjected tothe corresponding gamma characteristic as follows: $\begin{matrix}{\begin{pmatrix}X \\Y \\Z\end{pmatrix} = {\begin{pmatrix}{{Xr}\quad \max} & {{Xg}\quad \max} & {{Xb}\quad \max} \\{{Yr}\quad \max} & {{Yg}\quad \max} & {{Yb}\quad \max} \\{{Zr}\quad \max} & {{Zg}\quad \max} & {{Zb}\quad \max}\end{pmatrix}\begin{pmatrix}{\gamma \quad {r\lbrack R\rbrack}} \\{\gamma \quad {g\lbrack G\rbrack}} \\{\gamma \quad {b\lbrack B\rbrack}}\end{pmatrix}}} & (11)\end{matrix}$

[0018] where Xrmax, Yrmax and Zrmax are the X, Y and Z values when the Rphosphor produces the maximum brightness, Xgmax, Ygmax and Zgmax are theX, Y and Z values when the G phosphor produces the maximum brightness,and Xbmax, Ybmax and Zbmax are the X, Y and Z values when the B phosphorproduces the maximum brightness.

[0019] The RGB values to obtain desired XYZ values can be calculatedusing equation (11) as follows: $\begin{matrix}\begin{matrix}{\quad {{{matrix}\quad {transform}\quad \begin{pmatrix}R^{\prime} \\G^{\prime} \\B^{\prime}\end{pmatrix}} = {\begin{pmatrix}{{Xr}\quad \max} & {{Xg}\quad \max} & {{Xb}\quad \max} \\{{Yr}\quad \max} & {{Yg}\quad \max} & {{Yb}\quad \max} \\{{Zr}\quad \max} & {{Zg}\quad \max} & {{Zb}\quad \max}\end{pmatrix}^{- 1}\begin{pmatrix}X \\Y \\Z\end{pmatrix}}}} \\{\quad {{gamma}\quad {correction}\quad \begin{matrix}{\quad {R = {\gamma \quad {r^{- 1}\left\lbrack R^{\prime} \right\rbrack}}}} \\{\quad {G = {\gamma \quad {g^{- 1}\left\lbrack G^{\prime} \right\rbrack}}}} \\{\quad {B = {\gamma \quad {b^{- 1}\left\lbrack B^{\prime} \right\rbrack}}}}\end{matrix}}}\end{matrix} & (12)\end{matrix}$

[0020] The processing flow is illustrated in FIG. 36.

[0021] In this arrangement, an output profile computation unit 136computes matrix coefficients for matrix transform and gamma correctionvalues for gamma correction from the RGB values and the XYZ values andstores them into an output profile storage unit 137. A device valueconversion unit 138 makes matrix transform and gamma correction on theXYZ values using the matrix coefficients and the gamma correction valuesand outputs RGB values to the image display controller 134 for displayon the monitor.

[0022] The conventional color management system described abovespecifies D50 for the light source used on both the input side and theoutput side. Therefore, a color mismatching problem will arise when animage is shot under a light source different from D50 or when an outputimage is observed under a light source different from D50.

[0023] In the conventional color image recording and reproducing systemillustrated in FIG. 34, it is assumed that, on the shooting side, animage is converted to chromaticity values, such as XYZ values, to suitthe lighting on the observer side and then transmitted to the observerside.

[0024] An image, once converted to XYZ values, has no longer spectralinformation. Thus, on the observer side, no data conversion can be madeto suit the lighting.

[0025] Only the spectral data on light used in shooting and the spectraldata on light used in observation are used for color matching. In orderto increase the accuracy of color reproduction, therefore, it isrequired that an input image itself should have a certain amount ofspectral information.

[0026] For this reason, the image input device must be a multi-spectralcamera capable of capturing spectral images in many bands, which makesit difficult to shoot a subject in one shot. In addition, a capturedimage will involve a large amount of data.

[0027] In displaying a color corrected image on the monitor, offsetlight (light of monitor emitted when the input value is zero) andenvironment light (light of surrounding place where the monitor isinstalled) will have influence on color reproduction. Thus, satisfactorycolor reproduction is not necessarily achieved even if an output profileis created for the monitor by the conventional technique.

[0028] When the power is applied to the monitor and then RGB signalssuch that R=G=B=0 are applied to the monitor, the monitor screen willnot display black (X=Y=Z=0) due to the influence of offset light of themonitor.

[0029] In a place where the monitor is set, there generally exists somelight source or outdoor light (sun light) which illuminates the monitorscreen. Under such conditions, reflection from the monitor screen occursand hence it does not follow that X=Y=Z=0 even when the power is notapplied to the monitor. That is, the monitor offset light and theenvironment light are added to an image to be displayed on the monitor.The sum of the monitor offset light and the environment light isreferred hereinafter to as a bias value.

[0030] If a profile is created taking the bias value into account, thenaccurate color reproduction will be achieved. However, the offset lightand the environment light vary greatly with time. For example, theoffset light varies greatly until the monitor becomes stabilized fromwhen the power was applied thereto.

[0031] In addition, the bias value will vary greatly when a light sourceused as environment light is changed, or subjected to a change with thepassage of time, or the outdoor light varies. The recreation of theoutput profile with each variation of the offset light or environmentlight requires not only expert knowledge but also a large amount oftime.

BRIEF SUMMARY OF THE INVENTION

[0032] It is an object of the present invention to provide a colorreproduction device which makes image conversion while referencing imageinput device information, and color reproduction environment informationcontaining shooting- and observation-time lighting spectral informationand information concerning the statistical nature of the spectrum of asubject, allows the image shooting and reproducing sites to be remotefrom each other, and allows accurate color reproduction even when offsetlight and environment light vary.

[0033] To attain the object, there is provided a color reproductiondevice for outputting an image of a subject shot by an image inputdevice to an image output device in displayed or printed form, whichcomprises an input profile creation section for creating an inputprofile that conforms to information concerning the image input deviceand environment information containing shooting- and observation-timelighting data and information concerning the optical nature of thesubject, a device-independent color conversion section having an inputprofile operation section for causing the input profile to operate onthe image to convert it to a device-independent color image, and adevice value conversion section for causing an output profile created inaccordance with information concerning the image output device tooperate on the device-independent color image to convert it to devicevalues.

[0034] Additional objects and advantages of the invention will be setforth in the description which follows, and in part will be obvious fromthe description, or may be learned by practice of the invention. Theobjects and advantages of the invention may be realized and obtained bymeans of the instrumentalities and combinations particularly pointed outhereinafter.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

[0035] The accompanying drawings, which are incorporated in andconstitute a part of the specification, illustrate presently preferredembodiments of the invention, and together with the general descriptiongiven above and the detailed description of the preferred embodimentsgiven below, serve to explain the principles of the invention.

[0036]FIG. 1 is a schematic illustration of a first embodiment of acolor reproduction device of the present invention;

[0037]FIG. 2A show arrangements of the device-independent colorconversion unit, respectively, of FIG. 1;

[0038]FIG. 2B show arrangements of the device value conversion unit,respectively of FIG. 1;

[0039]FIG. 3 shows another arrangement of the color correction unit ofFIG. 1;

[0040]FIG. 4 shows an arrangement of the device independent colorconversion unit;

[0041]FIG. 5 is a diagram for use in explanation of a way of inputtingenvironmental information to the correction unit;

[0042]FIG. 6 is a diagram for use in explanation of a way of inputtingenvironmental information to the correction unit;

[0043]FIG. 7 shows an arrangement of the color correction unit which isseparated into a color correction preprocessing unit and a colorcorrection postprocessing unit;

[0044]FIG. 8 shows an arrangement for creating an input/output profileby concatenating an input profile and an output profile;

[0045]FIG. 9 shows a specific arrangement of the color reproductiondevice according to the first embodiment;

[0046]FIG. 10 is a schematic illustration of a second embodiment of thecolor reproduction device of the present invention;

[0047]FIG. 11 is a diagram for use in explanation of lightingconvertible image data which is inputted to a color correction unit of adevice according to a third embodiment;

[0048]FIG. 12 shows a format of lighting convertible image data used inthe third embodiment;

[0049]FIG. 13 shows a modification of the third embodiment;

[0050]FIG. 14 shows a format of lighting convertible image data used inthe modification of the third embodiment;

[0051]FIG. 15 shows, in appearance form, a first specific application ofthe device according to the third embodiment;

[0052]FIG. 16 shows, in block diagram form, an arrangement of the deviceof FIG. 15;

[0053]FIG. 17 shows, in appearance form, a second specific applicationof the device according to the third embodiment;

[0054]FIG. 18 shows, in block diagram form, an arrangement of thedigital camera of FIG. 17;

[0055]FIG. 19 shows, in block diagram form, an arrangement of the deviceof FIG. 17;

[0056]FIG. 20 shows an arrangement of a multi-spectral camera used in afourth embodiment of the color reproduction device of the presentinvention;

[0057]FIG. 21 shows a second arrangement of the multi-spectral cameraused in the fourth embodiment of the color reproduction device of thepresent invention;

[0058]FIG. 22 shows an arrangement of a multi-spectral camera used in afifth embodiment of the color reproduction device of the presentinvention;

[0059]FIG. 23 shows an arrangement of the device value conversion unitin a sixth embodiment of the color reproduction device of the presentinvention;

[0060]FIG. 24 is a conceptual diagram of the monitor screen in a seventhembodiment of the color reproduction device of the present invention;

[0061]FIGS. 25A, 25B and 25C shows the measurements of bias values usinga chromaticity meter in different environments in the seventhembodiment;

[0062]FIG. 26 shows an arrangement of the device value conversion unitin the seventh embodiment of the color reproduction device of thepresent invention;

[0063]FIGS. 27A and 27B are diagrams for use in explanation of achromaticity sensor used in an eighth embodiment of the presentinvention;

[0064]FIGS. 28A, 28B and 28C show modifications of the chromaticitysensor in the eighth embodiment;

[0065]FIG. 29 shows an arrangement of a ninth embodiment of the colorreproduction device of the present invention;

[0066]FIG. 30 shows an arrangement of a tenth embodiment of the colorreproduction device of the present invention;

[0067]FIG. 31 shows an arrangement of the device value conversion unitin an eleventh embodiment of the color reproduction device of thepresent invention;

[0068]FIG. 32 is a schematic illustration of a conventional colorreproduction device;

[0069]FIG. 33 shows an arrangement of the color correction unit in theconventional color reproduction device;

[0070]FIG. 34 shows an arrangement of a conventional color reproductiondevice in which a shooting site and a reproduction site are remote fromeach other;

[0071]FIG. 35 shows an arrangement of the output profile creation unitin the color correction unit in the conventional color reproductiondevice; and

[0072]FIG. 36 shows an arrangement for performing a sequence ofprocesses of matrix transform and gamma correction in the colorcorrection unit in the conventional color reproduction device.

DETAILED DESCRIPTION OF THE INVENTION

[0073] Reference will be made to FIGS. 1 through 7 to describe a firstembodiment of a color reproduction device of the present invention.

[0074] As shown in FIG. 1, the color reproduction device is composedroughly of an image input device 1 for capturing an image of a subject,a color correction unit 3 for correcting the colors of the image, and animage output device 2 for outputting (displaying or printing) an outputimage.

[0075] The color correction unit 3 is composed of a device independentcolor conversion unit 4 and a device value conversion unit 5.

[0076] The device independent color conversion unit 4 converts thecolors of an input image to device independent colors by making areference to an input profile 4 a, thereby producing a deviceindependent color image. The device value conversion unit 5 makes areference to an output profile 5 a to convert the device independentcolor image to an output image that have values that match thecharacteristics of the image output device 2.

[0077] The device independent color conversion unit 4 is constructed, asshown in FIG. 2A, from an input profile creation unit 6 and an inputprofile operation unit 7. The input profile creation unit 6 isresponsive to image input device information and environmentalinformation about a color reproduction environment to create and outputan input profile 4 a to the input profile operation unit 7. Theoperation unit 7 causes the input profile to operate on the input imageto provide image color conversion.

[0078] As shown in FIG. 4, the input profile creation unit 6 may bearranged as a matrix creation unit 9 and the input profile operationunit 7 may be arranged as a matrix operations unit 8. Thus, since aninput profile can be created by means of matrix operations, an inputimage can be converted into a device-independent color image at highspeed.

[0079] The color correction unit 3 includes, as shown in FIG. 3, aninput/output profile creation unit 11 and an input/output profileoperation unit 13 to create an input/output profile 12 from the inputprofile 4 a and the output profile 5 a. In this manner, the inputprofile 4 a and the output profile 5 a can be concatenated to make fastconversion from an input image to an output image.

[0080] The input profile creation unit 6, which creates an input profiletaking into account various items of information for creating a colorreproduced image, can convert an input image to a device-independentcolor image with accuracy.

[0081] The image input device information shown in FIG. 2 contains thecharacteristics of the image input device used in shooting and settingstates (hereinafter referred to as shooting characteristics). On theother hand, the environment information contains spectral dataconcerning lighting used in capturing an image of a subject with theimage input device (hereinafter referred to as shooting-time lightingdata), spectral data concerning a light source in the place where theimage of the subject is watched (hereinafter referred to asobservation-time lighting data), and information concerning thestatistical nature of the spectrum of the subject which was shot(hereinafter referred to as subject characteristics).

[0082] The use of the shooting characteristics permits a colorreproduced image of the subject shot by the image input device to beestimated with accuracy. Even if the image input device is amulti-spectral camera that captures a plurality of spectral images of asubject or a digital camera, color reproduction can be achieved.

[0083] The use of the shooting-time lighting data permits the effect oflighting at the shooting time to be canceled. That is, even if a subjectis shot under any lighting (for example, fluorescent lamp, incandescentlamp, sunlight, and so on), the accurate spectral reflectance of thesubject itself can be calculated. Also, the use of the observation-timelighting data permits colors under lighting in the place where thesubject image is actually watched to be calculated. The use of thesubject characteristics permits a color reproduced image to be estimatedwith accuracy even if an input image has little spectral information.

[0084] Next, the environmental information entered into the colorcorrection unit 3 will be described with reference to FIGS. 5 and 6.

[0085] The environmental information is provided from the image inputdevice 1, a dedicated input device 14, a network 15, or a storage medium16.

[0086] When the environmental information is input from the image inputdevice 1 or another input device, shooting-time environmentalinformation can be obtained in real time, which, even when theenvironment varies from hour to hour, allows an input profile thatprovides accurate conversion to a device-independent color image to becreated.

[0087] Where the environmental information is provided from the network15 or the storage medium 16, an input profile can be created to suit theenvironment at the remote site or the past environment.

[0088] As shown in FIG. 6, the color correction unit 3 is composedroughly of the device-independent color conversion unit 4 and the devicevalue conversion unit 5.

[0089] The input profile creation unit 6 in the device-independent colorimage conversion unit 4 comprises an lighting data select unit 18, asubject characteristic select unit 19, a shooting characteristic selectunit 20, and an input profile calculation unit 21.

[0090] The lighting data select unit 18, the subject characteristicselect unit 19, and the shooting characteristic select unit 20 receiveimage input device information and environment information from theinput device 14 or the like. The input profile calculation unit 21calculates input profile 4 a based on the outputs of the select units.The input profile operation unit 7 is composed of an input image selectunit 22 which makes a selection among input images and a colorconversion unit 23 which converts the selected image to adevice-independent color image on the basis of the input profile 4 a.

[0091] An output profile operation unit 24 in the device valueconversion unit 5 comprises a color conversion unit 25 which performs acolor conversion process on the device-independent color image on thebasis of the output profile 5 a to provide an output image, and anoutput device select unit 26 which selects an output device to which theoutput image is to be directed and then directs the output image toeither image output device 17, storage medium 16, or network 15.

[0092] The output profile creation unit 10 for creating the outputprofile 5 a is composed of an output device characteristic select unit27 which selects necessary information from output device informationand an output profile calculation unit 28 which calculates the outputprofile 5 a based on the selected output device characteristics.

[0093] The components in the present embodiment may be subjected tovarious modifications and variations.

[0094] For example, the image input device 1 may be a multi-spectralcamera using a plurality of bandpass filters, a multi-spectral camerausing a wavelength-variable filter using liquid crystals, amulti-spectral camera in which an optical path is split by means ofprisms, or a digital camera. The image output device 17 may be either aTV monitor, a projector, or a printer.

[0095] To obtain spectral data, a spectroscope or multi-spectral cameracan be used as the input device 14. The same system may be installed ata remote site on the network 15 for transmission of images andenvironmental information between the systems. As the storage medium,use is made of a floppy disk, a magneto-optical (MO) disk, or the like.

[0096] In such an arrangement, as shown in FIG. 7, the color correctionunit 3 may be separated into a color correction preprocessing section 3a and a color correction postprocessing section 3 b. In this case, anoutput device for a device-independent color image from the colorconversion unit 23 is selected by the output device select unit 31 inthe preprocessing section 3 a and then sent to the postprocessingsection 3 b via a storage medium 29 or a network 30. A selection is madeby the device independent color image select unit 32 in the outputprofile operation unit 24, and the selected image is subjected to colorconversion based on the output profile 5 a in the color conversion unit25.

[0097] This embodiment is sometimes effective in storing or transmittingimage data because the device-independent color image requires a smallerdata size than images in a format that allows lighting conversion. InFIG. 7, corresponding parts to those in FIG. 5 are denoted by likereference numerals and descriptions thereof are omitted.

[0098] Next, an arrangement in which the input profile 4 a and theoutput profile 5 a are combined into an input/output profile 12 will bedescribed with reference to FIGS. 8 and 3.

[0099] The input/output profile operation unit 13 in the colorcorrection unit 3 comprises an input image select unit 33 which makes aselection among input images and an input image conversion unit 34 whichconverts a selected input image based on the created input/outputprofile 12. The image subjected to conversion is directed to an outputdevice selected by an image output device select unit 35.

[0100] Such an arrangement requires that an input image be subjected toconversion one time only, thus further increasing the processing speedas compared with the arrangement of FIG. 6.

[0101]FIG. 9 shows a specific arrangement of the color reproductiondevice according to the first embodiment of the present invention. Thisembodiment, implemented in computer software, is an example of a systemarranged to produce and display a color reproduced image on a monitor.

[0102] As shown in FIG. 9, this system is composed of a multi-spectralcamera 41 which captures multi-spectral images of a subject 53,spectrometers 42 and 43, a monitor 44, a chromaticity meter 45 formeasuring the profile of the monitor 44, and a computer 46.

[0103] Of the sections implemented in software in the computer 46, thosefunctioning in the same way as those shown in FIG. 6 will be designatedat the same reference numerals as used in FIG. 6.

[0104] The computer 46 includes, in addition to the sections (software)for creating an input profile and an output profile, a multi-spectralimage shooting section 47 for capturing images by the multi-spectralcamera 41, a lighting data measurement section 48 for controlling thespectrometers 42 and 43 to obtain lighting data used for creating theinput profile 4 a, a monitor measurement section 49 for controlling thechromaticity meter 45 to obtain monitor data used for creating theoutput profile 5 a, and a color reproduced image display section 50 fordisplaying a color reproduced image on the monitor 44.

[0105] Such an arrangement requires to create the input and outputprofiles prior to a color reproduced image producing process.

[0106] In creating an input profile, shooting-time and observation-timelighting spectral data are measured using spectrometers 42 and 43. Eachof reference plates 51 and 52 used for measurement is simply a platewhose spectral reflectance is already known in order to get exactlighting spectral data. It is preferable to use a plate, such as astandard white plate, that has constant and high spectral reflectance,and little changes in characteristics with the passage of time.Although, in FIG. 9, there are illustrated an electric light bulb as ashooting light source and a fluorescent lamp as an observation lightsource, light sources of the same type may be used. Measurement may bemade using sunlight as opposed to artificial light.

[0107] The shooting characteristics of the multi-spectral camera 41calculated from the lighting data measured by the lighting datameasurement section 48, and the subject characteristics are entered intothe input profile creation section 6 to create an input profile 4 a. Thecreated input profile may be stored on a memory or disk not shown, inwhich case it will be read into the computer when it is needed.

[0108] The output profile 5 a can be created by displaying appropriatecolors on the monitor 44 and measuring them with the chromaticity meter45. More specifically, the chromaticity values of the phosphors of themonitor 44 and a relationship between digital values for RGB signalsinput to the monitor and actual brightness value (generally known asgamma characteristic) are calculated.

[0109] The output profile 5 a is created by the output profile creationsection 10 on the basis of data measured by the monitor measurementsection 49. Like the input profile 4 a, the created output profile 5 ais stored on a memory or disk and read into the computer when needed.

[0110] In this embodiment, a chromaticity meter is provided for monitormeasurement; otherwise, the spectrometer for measuring lighting may beused as a chromaticity meter as well.

[0111] To produce a color reproduced image of a subject, the subject 53is shot by the multi-spectral camera 41 and the resultant subject imageis operated on by the input profile 4 a and the output profile 5 a insequence to produce an image that suits the characteristics of themonitor 44. The multi-spectral camera may be either a multi-spectralcamera that has a rotating color filter composed of a plurality ofbandpass filters or a multi-spectral camera that uses a transmittedwavelength-variable filter.

[0112] When the input profile 4 a is so designed as to processthree-dimensional data, a normal RGB camera or digital camera can alsobe used.

[0113] In the present embodiment, the color reproduction device isimplemented by a single personal computer. A color reproduction deviceor system can also be implemented which transmits accurately colorsamong multiple personal computers connected to a network.

[0114] Hereinafter, an example of an algorithm for software processingwill be described. First, let an output signal of the multi-spectralcamera be denoted by gi. Then, gi is represented by

gi=∫e _(m)(λ)·f(λ)·h _(i)(λ)·dλ  (1)

[0115] where em(λ) is the spectrum of shooting lighting, f(λ) is thespectral reflectance, and hi(λ) is the multi-spectral camera sensitivitywhen filter i is used. Actually, the tristimulus values, X, Y, Z, when asubject is observed by human are given by

X=∫e ₀(λ)·f(λ)·x(λ)·dλ

Y=∫e ₀(λ)·f(λ)·y(λ)·dλ

Z=∫e ₀(λ)·f(λ)·z(λ)·dλ  (2)

[0116] where e₀(λ) is the lighting spectrum at the time of observation,f(λ) is the spectral reflectance of the subject, and x(λ), y(λ), andz(λ) are each an isochromatic function. A matrix M is then calculated tosatisfy

M·g=[X, Y, Z] ^(t)  (3)

[0117] where t represents the transpose of a matrix.

[0118] An evaluation function designs M so as to minimize

e ² =E[(X−M·g)²]  (4)

[0119] where E[ ] represents an operator for seeking an expected value.

[0120] M sought as

∂e ² /∂M=0  (5)

[0121] is the least square filter given by

M=A·B ⁻¹

A _(ij) =∫∫e ₀(λ)·x _(i)(λ)·E[f(λ)·f(λ′)]·e _(m)(λ′)·h _(j)(λ′)·dλ·dλ′

B _(ij) =∫∫e _(m)(λ)·h _(i)(λ)·E[f(λ)·f(λ′)]·e _(m)(λ′)·h_(j)(λ′)·dλ·dλ′  (6)

[0122] E[f(λ)·f(λ′)] in equation (6) represents a spectral correlationterm of the subject to be measured. To minimize the evaluation functionfor every possible objects, spectral correlation term will be a unitmatrix. Therefore matrix M is given by

M=A·B ⁻¹

A _(ij) =∫e ₀(λ)·x _(i)(λ)·e _(m)(λ)·h _(j)(λ)·dλ

B _(ij) =∫e _(m)(λ)² ·h _(i)(λ)·h _(j)(λ)·dλ  (7)

[0123] If some restrictions are imposed on subjects to be reproduce, andthe spectral reflectance of the subject can be represented by someprinciple components, colors can be estimated with accuracy even from asmall number of spectral images. For example, in the field of remotemedical systems, when the spectral reflectance of skin is measured and acorrelation matrix is then calculated as the statistical nature, theskin color can be reproduced with accuracy from a small number ofspectral images.

[0124] That is, for color reproduction processing using subjectcharacteristics, the creation of an input profile corresponds to thecalculation of equation (6). When no subject characteristics are used,the input profile creation corresponds to the calculation of equation(7). The input profile operation section multiplies signals obtained inthe multi-spectral image shooting section by filter M, namely,calculates equation (3).

[0125] Next, a second embodiment of the color reproduction device of thepresent invention will be described.

[0126] As shown in FIG. 10, the second embodiment is constructed from animage input device 1, a device-independent color conversion unit 4, adevice value conversion unit 5, an image output device 2, and aninformation database 54.

[0127] The device-independent color conversion unit 4 converts the imageof a subject shot by the image input device 1 to a device-independentcolor image by referencing an input profile 4 a. The device valueconversion unit 5 converts the resulting device-independent color imageto device values that suit the characteristics of the image outputdevice 2 by referencing an output profile 5 a, thereby producing anoutput image. The output image is outputted (displayed or printed) bythe image output device 2. Such image input device information andenvironmental information as described previously are entered into thedatabase 54, thus allowing the image input device information orenvironmental information to be referenced freely at the time ofcreating the input profile.

[0128] Thus, in any environment an input image can be converted to adevice-independent color image. The information database may be retainedat the other end of the network, or on a storage medium, such as aCD-ROM, and, at the time of input profile creation, called forreference. An information database for information concerning the imageoutput device may be provided for reference at the time of creating theoutput profile. Thus, a device-independent color image can be convertedto an output image in any environment.

[0129] A third embodiment of the color reproduction device of thepresent invention will be described next with reference to FIGS. 11 and12.

[0130] In the third embodiment, an input image itself has part of imageinput device information or environmental information needed to createan input profile, and color conversions are made on image data having adata structure that allows lighting conversion.

[0131] The third embodiment is constructed, as shown in FIG. 11, from animage input device 1, a color correction preprocessing unit 3 c, a colorcorrection unit 3 d, and an image output device 2.

[0132] Upon receipt of an image of a subject shot by the image inputdevice 1, color correction preprocessing unit 3 c combines the inputimage data and various information necessary for creation of an inputprofile into an image format that allows color corrections on changes incolor due to the effect of lighting, the image format being referred toas the lighting convertible image format. The color correction unit 3 dcauses input and output profiles to operate on the lighting convertibleimage data 55 from the preprocessing unit 3 c to produce color-correctedimage data, which, in turn, is outputted (displayed or printed) from theimage output device 2.

[0133] The color correction unit 3 d is composed of an input datadivision unit 59, a device-independent color conversion unit 4, and adevice value conversion unit 5.

[0134] The input data division unit 59 divides input lightingconvertible image data 55 into image data and various informationnecessary for input profile creation, which are then applied to thedevice-independent color conversion unit 4. The conversion unit causesthe input profile to operate on the image data to output adevice-independent color image. The device value conversion unit 5converts the device-independent color image to device values that matchthe characteristics of the output device by referencing the outputprofile.

[0135] The device-independent color conversion unit 4 comprises an inputprofile creation section 6 responsive to the image input deviceinformation and the environmental information for creating an inputprofile, and an input profile operation section 7 for causing the inputprofile to operate on the input image data for conversion to adevice-independent color image.

[0136] For example, as shown in FIG. 12, the lighting convertible imagedata 55 comprises image data 55 a, a plurality of images assigned toband numbers, shooting-time lighting data 55 b as environmentalinformation, filter information 55 c 1 and shutter speed information 55c 2 used in the image input device as image input device information,and header information 55 d.

[0137] In this arrangement, image data itself inputted to thedevice-independent color conversion section 4 contains part of the imageinput device information and environmental information. Image inputdevice information and environmental information which are not containedin the input image data are externally applied to the conversion section4 as in the previous embodiments.

[0138] Therefore, by combining image data and part of image input deviceinformation and environmental information in the color correctionpreprocessing section 3 c into a single data structure, data can beobtained which allows observation-time lighting to be changed freely.Such an arrangement as shown in FIG. 8 may be used in place of thedevice-independent color conversion section 4 and the device valueconversion section 5.

[0139]FIGS. 13 and 14 show a modification of the third embodiment.

[0140] In this modification, the color correction section shown in FIG.7 is separated into a preprocessing section and a postprocessingsection. Between the preprocessing and postprocessing sections, imagedata is converted into an image data format (this is also the lightingconvertible image format) that approximates the spectral reflectance ofa subject for subsequent movement or transmission.

[0141] This modification is constructed from an image input device forshooting a subject to produce a subject image, a color correctionpreprocessing section 3 e having an image format conversion section 56for converting the input image into image data (lighting convertibleimage) that approximates the spectral reflectance of the subject byreferencing an input profile A 57 and adding header information to theimage data, a color correction section 3 f having a device-independentcolor image conversion section 4 for converting lighting convertibleimage data 58 comprising the image data and the header information intoa device-independent color image by referencing an input profile B 4 aand a device value conversion section 5 for converting the resultingdevice-independent color image to device values that match thecharacteristics of the image output device 2 by referencing an outputprofile 5 a to provide an output image, and an image output device 3 foroutputting (displaying or printing) the output image.

[0142] This color reproduction device is characterized by converting theformat of an input image so as to contain shooting characteristics andshooting-time lighting data to thereby provide a lighting convertibledata structure that approximates the spectral reflectance of a subject.

[0143] As an example of lighting convertible image data 58 representedby the lighting convertible image format, there is illustrated in FIG.14 a format of image data representing the spectral reflectance of asubject.

[0144] By converting an input image to image data containing shootingcharacteristics and shooting-time lighting data (image dataapproximating the spectral reflectance of a subject) in the colorcorrection preprocessing section 3 e, this modifications allows dataquantity to be reduced as compared with the image data format of FIG. 11in the third embodiment, thus increasing the processing speed.

[0145] Next, specific arrangements of the third embodiment will bedescribed.

[0146]FIGS. 15 and 16 show a first specific arrangement of the thirdembodiment.

[0147] To confirm color samples of a commodity using a personalcomputer, this arrangement employs a storage medium that is recordedwith image data pertaining to the commodity in a data format that allowschanges in lighting and a database for various lighting data.

[0148] For example, on a CD-ROM 60 as the storage medium are retainedcommodity catalog viewer software, a lighting database that containsinformation concerning lighting assumed to be installed in a place toview the commodity, and image data pertaining to the commodity (lightingconvertible image data).

[0149] The arrangement comprises the CD-ROM 60 recorded with thecommodity catalog viewer software, the lighting database, and image datapertaining to the commodity in a data format allowing lighting changes,a personal computer 61 that runs the commodity catalogue viewersoftware, a lighting sensor 62 that detects lighting in the place wherethe personal computer is installed, and a monitor 63 for displaying animage from the personal computer.

[0150] The personal computer 61 contains an output profile selectsection 64 that selects a suitable one out of a plurality of outputprofiles which have been set up in advance, an observation lightingselect section 65 responsive to the lighting database and a detectedsignal from the lighting sensor 62 for selectively outputting datanecessary for color correction, and a color correction section 66 thatmakes color corrections on the image data of the subject by referencinginput and output profiles to provide an output image to the monitor. Thearrangement further includes a hard disk, a ROM, a RAM, and so on, whichare needed to run the viewer software.

[0151] The input profile may be created in the color correction sectionfrom the image data and data from the lighting database. Alternatively,the input profile may have been created in advance and stored in amemory.

[0152] In this arrangement, the user loads the CD-ROM 60 into thepersonal computer 61, activates the commodity catalog viewer software,and displays the commodity catalog. At this point, lighting data is alsoretrieved from the lighting database. Thus, the user can view how thecommodity changes in color if it were placed under fluorescent lamp,incandescent lamp, or sunlight, and so on. Further, by attaching alighting sensor to the personal computer, it is also possible toreproduce the color of the commodity in the place where the personalcomputer is installed. In addition, an object movie that allows an imageto be viewed from various angles and image data that allows changes inlighting (lighting convertible image data) may be used in combination.

[0153] In this embodiment, a storage medium is used to provide imagedata; otherwise, the Internet may be used. The commodity is not limitedto clothing. This embodiment is also effective in confirming the colorsof cosmetics, furniture, electrical appliances, pictures, and so on.

[0154] Next, a second specific example of the third embodiment will bedescribed with reference to FIGS. 17, 18 and 19.

[0155] As shown in FIG. 17, this arrangement includes a digital camerain addition to the components of FIGS. 15 and 16. An image captured bythe digital camera is fit into image data pertaining to a commodity readfrom the CD-ROM and the user changes lighting freely.

[0156] The digital camera 67 is constructed, as shown in FIG. 18, from alens 68, an image pickup device 69 for converting an image obtainedthrough the photoelectric effect into electrical signals, a signalprocessing unit 70 for processing image information consisting of theelectrical signals, a shooting characteristic storage unit 71 forstoring the shooting characteristics of the camera, a lighting sensor 72for detecting the lighting at a shooting site, a shooting-time lightingdata detect unit 73 for processing a detected signal from the sensor,and a memory card 74 for storing the subject image data, the shootingcharacteristics, and the shooting-time lighting data. The memory card isremovably attached to the camera.

[0157] The color reproduction device is constructed from the CD-ROM 60recorded with the commodity catalog viewer software, the lightingdatabase, and lighting convertible image data, the personal computer 61for running the viewer software, the lighting sensor 62 for detectingthe lighting at the personal computer installation, the memory card 74recorded with image data captured by the digital camera 67, a subjectcharacteristic database 76 for storing subject characteristic, and aprivate clothing database 77. The databases 76 and 77 are retained on ahard disk.

[0158] The personal computer 61 includes, in addition to the componentsin the first specific arrangement, a subject designation section 78 fordesignating data corresponding to a subject in the subjectcharacteristic database 76, a color correction section 79 for makingcolor corrections on subject image data read from the memory card inaccordance with shooting-time lighting data and shooting characteristicswhich are also read from the memory card, and an image combining section80 for combining independently color-corrected images.

[0159] In the color reproduction device thus arranged, when thecommodity catalog viewer software is activated to display clothes, aportrait (67 a) of the user shot by the digital camera 67 and the imageof clothing can be combined (67 b).

[0160] User can construct clothing database 77, which has image data ofclothes user owned. Using coordinate software together, user cansimulate coordination of clothes when user bought the new cloth incatalog.

[0161] In this embodiment, a storage medium is used to provide imagedata; instead, the Internet may be used. The commodity is not limited toclothing. This embodiment is also effective in confirming the colors ofcosmetics, furniture, electrical appliances, pictures, and so on.

[0162] Next, a fourth embodiment of the color reproduction device of thepresent invention will be described.

[0163] This embodiment comprises an image input device capable ofdetermining part of environmental characteristics at the same time asubject is shot, color correction unit 3, and an image output device 2.

[0164] In FIG. 20 there is illustrated the arrangement of amulti-spectral camera that captures an image of a subject and part ofenvironmental information at the same time.

[0165] In this arrangement, a beam of light collected by an objectivelens 81 is split by a beam splitter 82 into tow beams: one is directedonto a CCD 84 and the other is reflected by a mirror 83 onto aspectrometer 85.

[0166] The multi-spectral camera captures a plurality of spectral imageswhile rotating a turret 86, having a plurality of bandpass filters bymeans of a motor 87.

[0167] While the spectral images are captured, the spectrometer 85measures the spectrum of a certain spot on the subject a plurality oftimes to obtain the statistical nature of the spectrum of the subject,which is sent to a subject characteristic calculation unit 88 b. Thatis, the image data and the subject characteristics of the environmentalinformation can be captured simultaneously.

[0168]FIG. 22 shows a modification of the camera shown in FIG. 21.

[0169] In this camera, a spectrometer 59 is placed on top of the camera.A shooting-time lighting data calculation unit 88 b calculatesshooting-time lighting data from spectral data obtained by thespectrometer 59. That is, according to this type of camera, image dataand shooting-time lighting data, which is part of environmentalinformation, can be captured at the same time.

[0170] In this embodiment, use may be made of a multi-spectral camerausing a plurality of bandpass filters, a multi-spectral camera using avariable-wavelength filter made of liquid crystal, a multi-spectralcamera in which the optical path of a beam of light is divided by meansof a prism, or a digital camera.

[0171] A fifth embodiment of the color reproduction device of thepresent invention will be described hereinafter.

[0172] This embodiment is constructed from an image input device 1, adevice-independent color conversion unit 4, a device value conversionunit 5, and an image output device 2, which remain unchanged from thosedescribed so far.

[0173] The device-independent color conversion unit 4 converts an inputimage into a device-independent color image by referencing an inputprofile 4 a, and the device value conversion unit 5 converts thedevice-independent color image to device values that match thecharacteristics of the image output device by referencing an outputprofile 5 a. An output image is outputted (displayed or printed) by theimage output device.

[0174] The image input device 1 that captures the image of a subject isequipped with a shooting information storage unit that stores all orpart of image input device information, which can be referenced freelyat the time of color correction.

[0175] In FIG. 22 there is illustrated a multi-spectral camera thatserves as the image input device 1.

[0176] The multi-spectral camera is constructed from an objective lens81, a lens controller 93 for drive controlling the lens, an image pickupdevice (CCD) 84, a rotating filter turret 86 comprising a plurality ofbandpass filters used in capturing images in different wavelength bands,a motor 87 for rotating the filter turret 86, a filter characteristicstorage unit (shooting characteristic storage unit) 90, provided foreach filter turret, for storing the characteristics of the filtersmounted, a filter characteristic read unit 91 for reading the filtercharacteristics, and a shooting characteristic converting section 92 forconverting lens information, shutter speed control and filtercharacteristics to shooting characteristics.

[0177] The filter characteristics are read into the filtercharacteristic read unit 91 each time the characteristics of filtersmounted on the filter turret 86 or the filter turret is exchanged.

[0178] Information concerning the objective lens 81 is read from thelens controller 93. The filter characteristic information and the lensinformation are converted into shooting characteristic data in theshooting characteristic conversion unit 92, which, in turn, is sent tothe color reproduction device. Data to be stored in the camera maycontain the spectral sensitivity characteristics of the CCD 84.

[0179] The camera used in this embodiment may be a multi-spectral camerausing a plurality of bandpass filters, a multi-spectral camera using avariable-wavelength filter made of liquid crystal, a multi-spectralcamera in which the optical path of a beam of light is divided by meansof a prism, or a digital camera.

[0180] A sixth embodiment of the color reproduction device of thepresent invention will be described next.

[0181] The sixth embodiment is the same as the arrangement shown in FIG.1 except the device value conversion unit 5.

[0182] As shown in FIG. 23, the device value conversion section 5comprises an output profile creation section 10 for creating an outputprofile 5 a in accordance with input image output device information, anoffset subtraction section 94 for subtracting offset from an inputdevice-independent color image, and an output profile operation section24 for performing a color conversion process on the output of the offsetsubtraction section by referencing the output profile 5 a.

[0183] Usually, offset light and environment light are added to an imagebeing displayed. $\begin{matrix}{\begin{pmatrix}X \\Y \\Z\end{pmatrix} = {{\begin{pmatrix}{{Xr}\quad \max} & {{Xg}\quad \max} & {{Xb}\quad \max} \\{{Yr}\quad \max} & {{Yg}\quad \max} & {{Yb}\quad \max} \\{{Zr}\quad \max} & {{Zg}\quad \max} & {{Zb}\quad \max}\end{pmatrix}\begin{pmatrix}{\gamma \quad {r\lbrack R\rbrack}} \\{\gamma \quad {g\lbrack G\rbrack}} \\{\gamma \quad {b\lbrack B\rbrack}}\end{pmatrix}} + \begin{pmatrix}X_{0} \\Y_{0} \\Z_{0}\end{pmatrix}}} & (8)\end{matrix}$

[0184] As can be seen from equation (8), the resulting X, Y, or Z valueis represented by the corresponding RGB values plus a bias value (X0,Y0, or Z0).

[0185] Thus, only the bias values related to offset light andenvironment light are measured and the bias values are subtracted fromXYZ values inputted to the profile. This process allows an outputprofile sought in dark room to be used as it is; thus, much work is notneeded to create an profile. Specifically,

[0186] matric transform $\begin{matrix}{\quad {{\begin{pmatrix}R^{\prime} \\G^{\prime} \\B^{\prime}\end{pmatrix} = {\begin{pmatrix}{{Xr}\quad \max} & {{Xg}\quad \max} & {{Xb}\quad \max} \\{{Yr}\quad \max} & {{Yg}\quad \max} & {{Yb}\quad \max} \\{{Zr}\quad \max} & {{Zg}\quad \max} & {{Zb}\quad \max}\end{pmatrix}^{- 1}\begin{pmatrix}{X - X_{0}} \\{Y - Y_{0}} \\{Z - Z_{0}}\end{pmatrix}}}\quad {{gamma}\quad {correction}\quad \begin{matrix}{\quad {R = {\gamma \quad {r^{- 1}\left\lbrack R^{\prime} \right\rbrack}}}} \\{\quad {G = {\gamma \quad {g^{- 1}\left\lbrack G^{\prime} \right\rbrack}}}} \\{\quad {B = {\gamma \quad {b^{- 1}\left\lbrack B^{\prime} \right\rbrack}}}}\end{matrix}}}} & (9)\end{matrix}$

[0187] As indicated in this equation, it is only required to subtractthe bias values (X0, Y0, Z0) from colors to be displayed before theoutput profile is operated on.

[0188] A seventh embodiment of the color reproduction device of thepresent invention will be described next.

[0189] Usually, monitor offset light and environment light are measuredseparately or simultaneously and then subtracted from XYZ values to bedisplayed. Let XYZ values associated with monitor offset light bedenoted by Ox, Oy, and Oz, and XYZ values associated with environmentlight be denoted by Lx, Ly, and Lz. Then, bias values X0, Y0, and Z0 aregiven by

X ₀ =O _(x) +L _(x)

Y ₀ =O _(y) +L _(y)

Z ₀ =O _(z) +L _(z)  (10)

[0190]FIG. 24 is a conceptual diagram of the monitor screen surface.

[0191]FIGS. 25A, 25B and 25C illustrate arrangements for measuring biasvalues using a chromaticity meter.

[0192] In the arrangement of FIG. 25A, to measure the XYZ values, Ox,Oy, Oz, associated with monitor offset light, a monitor and achromaticity meter are installed in a dark room and chromaticity valuesare detected with the power to the monitor turned on and monitor inputsset such that R=G=B=0. In FIG. 25B, XYZ values, Lx, Ly, Lz, associatedwith environment light are measured. In FIG. 25C, bias values X0, Y0 andZ0 are measured directly.

[0193]FIG. 26 shows the arrangement of the device value conversion unitof FIG. 23 and its peripheral units.

[0194] The device value conversion unit 5 is constructed fromsubtracters 97 a, 79 b, and 79 c, a matrix transform section 98, andgamma correction sections 99 a, 99 b, and 99 c.

[0195] The subtracters 97 a, 79 b, 79 c subtract bias values X0, Y0, andZ0 from input values X, Y, and Z, respectively. The bias values X0, Y0and Z0 are represented by equation (10) on the basis of Lz, Ly and Lxvalues from storage 95 and Ox, Oy, and Oz values from storage 96. Thematrix transform section 98 performs matrix transformation on theresulting X, Y, and Z values using matrix coefficients read fromcoefficient storage in accordance with equation (9). The gammacorrection sections 99 a, 99 b and 99 c make gamma corrections on thematrix-transformed R′, G′, and B′, respectively. For the output profilestorage, refer to FIG. 36.

[0196] In the case where bias values are obtained directly as shown inFIG. 25C, a bias memory 100 is provided for storing these bias values.For the above subtraction processing, the bias values stored in thismemory are used as shown in FIG. 26C.

[0197] In this embodiment, since there is no need to change the outputprofile, it can be operated on very easily and fast.

[0198] An eighth embodiment of the color reproduction device of thepresent invention will be described next.

[0199] In this embodiment, a bias sensor is provided for detecting bothof monitor offset light and environment light.

[0200] As shown in FIG. 27A, a chromaticity sensor 101 is brought intocontact with the monitor display screen to detect offset light. Todetect environment light, as shown in FIG. 27B, an environment lightdetecting adapter 102 is attached to the sensor 101 and the sensor ismounted on the top of the monitor.

[0201] In this case, since the chromaticity values obtained from thesensor are not ones resulting from reflection from the monitor screen,these values are converted by the environment light calculation unit toXYZ values, Lx, Ly, and Lz, associated with environment light.

[0202] The monitor offset light becomes stabilized a short time afterthe power has been applied to the monitor. On the other hand,environment light changes very greatly, especially if outdoor lightcomes.

[0203] According to the arrangement of FIG. 27B, even if the environmentlight changes rapidly, the change can be detected momentarily, andstabilized color reproduction can be implemented all the time.

[0204]FIGS. 28A and 28B show an arrangement of a chromaticity sensorcapable of detecting both the offset light and the environment light.The sensor is provided with windows 103 a and 103 b which face eachother and allow offset light and environment light to pass through,respectively. On the window 103 b for environment light is mounted anenvironment light detecting adapter 102. Between the windows is placed arotating mirror 104 which bends light coming through a window to achromaticity sensor 105 placed underneath. By rotating the mirror 104,switching is made between offset light detection and environment lightdetection.

[0205]FIG. 28C shows a modification. This arrangement is equipped with amirror 107 between the windows and chromaticity sensor 105 and spectrumsensor 106 placed underneath, allowing concurrent detection of monitoroffset light and environment light. Since the spectrum of environmentlight can be detected, the detected data can be used as observation-timelighting data serving as environmental information necessary forcreating an input profile.

[0206] A ninth embodiment of the color reproduction device of thepresent invention will be described next.

[0207] As shown in FIG. 29, the ninth embodiment has a chromaticitymeter mounted on a hood for shielding the monitor from environmentlight.

[0208] If the effect of environment light is too great, it is impossibleto perform accurate color reproduction irrespective of theabove-described processing for environment light and offset light. In aplace where accurate color reproduction is a requirement, as in amedical site where diseased parts must be identified accurately, a hood109 will inevitably be attached to a monitor 108 to remove the effect ofenvironment light.

[0209] In this arrangement, therefore, a chromaticity meter 101 isattached to the environment light shielding hood 109 to detect biasvalues.

[0210] In this arrangement, when a reset button 110 is pressed, an imageof R=G=B=0 is displayed on the monitor 108, so that bias values X0, Y0and Z0 are measured with the chromaticity meter 101. The effect ofenvironment light is not only reduced by the use of the hood 109 butalso removed by the above-described processing, which allows accuratecolor reproduction.

[0211] This embodiment is arranged to detect the bias values at the timewhen the reset button 110 is pressed. Alternatively, an R=G=B=0 imagemay be displayed at all times on a portion of the monitor screen, forexample, at its lower right portion, to always update the bias values inaccordance with variations in environment light.

[0212] Depending on the portion of the monitor screen, the bias valuesmay vary. In such a case, instead of the chromatically meter a cameracapable of measuring XYZ values may be attached to obtain bias valuesfor each of pixels on the monitor or for each block of pixels. Theresulting pixel- or block-dependent bias values are subtracted in thesubtracters 97. When the hood 109 is used, environment light is reducedat the upper portion of the monitor screen but its lower portion isstill affected by the environment light. In this case, if bias valuesthat depend on the position on the monitor screen are used, thenaccurate color reproduction will be performed throughout the monitorscreen.

[0213] Next, a tenth embodiment of the color reproduction device of thepresent invention will be described.

[0214] This embodiment eliminates the need for a chromaticity meter atprofile creation time by preparing information necessary for profilecreation beforehand within the monitor.

[0215] As shown in FIG. 30, the monitor 110 is equipped with a timemeasurement unit 111 for measuring the operating time of the monitor, athermometer 112 for measuring the temperature of the monitor, an RGBphosphor XYZ value storage unit 113 for storing the XYZ chromaticityvalues of the RGB phosphors, and a tone curve data storage 114 forstoring tone curve data. There are further provided a contrast control115 and a brightness control 116.

[0216] An output profile calculation unit 117 comprises a matrixcoefficient calculation unit 118 and a gamma correction calculation unit119. An output profile storage unit 120 comprises a matrix coefficientstorage unit 121 and RGB gamma correction tables 122 a, 122 b and 122 c.

[0217] In the storage units in the monitor, RGB phosphor XYZchromaticity values and tone curve data under various conditions arestored. By referring to selected XYZ chromaticity values and tone curvedata, the output profile calculation unit provides matrix coefficientsand gamma correction values. The various conditions are the overalloperating time of the monitor since it was manufactured, thetemperature, and contrast and brightness values.

[0218] This embodiment allows an output profile to be operated on veryeasily because it is created without using a chromaticity meter.

[0219] In this embodiment, the RGB phosphor XYZ chromaticity values andtone curve data under various conditions are stored inside the monitor;otherwise, they may be stored as file data in a personal computer andread when necessary.

[0220] Next, an eleventh embodiment of the color reproduction device ofthe present invention will be described. This embodiment is described interms of a device value conversion unit for make corrections on biasvalues using tables in referencing an output profile.

[0221] The device value conversion unit, as shown in FIG. 31, comprisesRGB tables 123, 124, and 125 each serving as an output profile andsubtracters 126 for subtracting bias values X0, Y0 and Z0 from input XYZvalues.

[0222] Thus, each of RGB values which correspond to input XYZ values canbe outputted in accordance with the output profile in the correspondingtable.

[0223] This embodiment and the seventh embodiment are effective formonitors that satisfy equation (11). Some monitors do not satisfyequation (11).

[0224] For such monitors, a known method is effective which stores RGBvalues corresponding XYZ values in tables. The bias values are correctedby, as in the seventh embodiment, subtracting bias values X0, Y0 and Z0from X, Y, and Z values and then referencing the tables.

[0225] This embodiment, while using tables in referencing outputprofiles, can correct bias values associated with offset light andenvironment light well.

[0226] As described so far, the color reproduction devices of thepresent invention makes image conversion with reference to image inputdevice information, and color reproduction environmental informationcomprising shooting-time and observation-time lighting spectral data,and information concerning the statistical nature of spectrum of asubject, and allows an output profile to be operated on an input imageat high speed even when offset light and environment light vary, therebyachieving accurate color reproduction. Also, an image captured by animage input device can be reproduced at a remote reproduction site.

[0227] Additional advantages and modifications will readily occur tothose skilled in the art. Therefore, the invention in its broaderaspects is not limited to the specific details and representativeembodiments shown and described herein. Accordingly, variousmodifications may be made without departing from the spirit or scope ofthe general inventive concept as defined by the appended claims andtheir equivalents.

1. A color-reproduction device allowed to accurately achieve colorreproduction with an image output device for displaying an image with aninput signal value, comprising: bias-value storing means for storing achromaticity value of offset light of the image output device and/or achromaticity value of environment light which is incident on a displaysurface of the image output device; and subtracting means forsubtracting, from a chromaticity value regarding the input signal value,the chromaticity value of the offset light stored in the bias-valuestoring means and/or the chromaticity value of the environment lightstored in the bias-value storing means.
 2. The color reproduction deviceaccording to claim 1, wherein the chromaticity value of the offset lightstored in the bias-value storing means is a chromaticity value which isobtained by sensing the display surface of the output device by use of achromaticity value detection sensor, after the image output device andthe chromaticity value detection sensor are placed in a darkroom, and apower supply is turned on when the input signal value is zero.
 3. Thecolor reproduction device according to claim 1, wherein the chromaticityvalue of the environment light stored in the bias-value storing means isa chromaticity value which is obtained by sensing the display surface ofthe image output device by use of the chromaticity value detectionsensor, when illumination light is incident on the display surface ofthe image output device, with a power supply turned off.
 4. The colorreproduction device according to claim 1, wherein the input signal valueis a chromaticity value obtained by adding the chromaticity value of theoffset light and the chromaticity value of the environment light, and abias value stored in the bias-value storing means is a chromaticityvalue which is obtained by sensing the display surface of the imageoutput device by use of a chromaticity value detection sensor, whenillumination light is incident on the display surface of the imageoutput device, with a power supply turned on when the input signal valueis zero.
 5. The color reproduction device according to claim 4, whereinwhen the chromaticity value detection sensor detects the chromaticityvalue of the environment light stored in the bias-value storing means,an environment light detection adaptor is attached to the chromaticityvalue detection sensor.
 6. The color reproduction device according toclaim 4, wherein: the chromaticity value detection sensor for detectingthe Chromaticity value of the environment light stored in the bias-valuestoring means and the chromaticity value detection sensor for detectingthe chromaticity value of the offset light stored in the bias-valuestoring means include identical casings, an optical axis of an opticalsystem is switched by a rotating mirror; and the chromaticity valuedetection sensor for detecting the chromaticity value of the environmentlight stored in the bias-value storing means detects the chromaticityvalue of the environment light via an environment detection adaptor. 7.The color reproduction device according to claim 4, wherein: thechromaticity value detection sensor for detecting the chromaticity valueof the environment light stored in the bias-value storing means and thechromaticity value detection sensor for detecting the chromaticity valueof the offset light stored in the bias-value storing means haveidentical housings; an optical system has two optical axes provided by amirror; and a direction in which the chromaticity value of the offsetlight is detected is opposite to that in which the chromaticity value ofthe environment light is detected.
 8. The color reproduction deviceaccording to claim 2, wherein the chromaticity value detection sensor isallowed to measure spectrum data.
 9. The color reproduction deviceaccording to claim 3, wherein the chromaticity value detection sensor isallowed to measure spectrum data.
 10. The color reproduction deviceaccording to claim 4, wherein the chromaticity value detection sensor isallowed to measure spectrum data.
 11. A color reproduction deviceallowed to accurately achieve color reproduction with an image outputdevice for displaying an image with an input signal value, comprising:tone curve storing means for storing tone curves according to variousconditions, condition detecting means for detecting one of the variousconditions; and γ correction calculating means far reading the tonecurve from the tone curve storing means based on said one of theconditions which is detected by the condition detecting means and thenperforming γ correction.
 12. The color reproduction device according toclaim 11, wherein one of the various conditions is usage time of theimage output device.
 13. The color reproduction device according toclaim 11, wherein one of the various conditions is a temperature of theimage output device.
 14. The color reproduction device according toclaim 11, wherein one of the various conditions is one of a contrast andbrightness of the image output device.